NCX1 Exchanger Cooperates with Calretinin to Confer Preconditioning-Induced Tolerance Against Cerebral Ischemia in the Striatum.

Recently, the Na(+)/Ca(+2) exchanger NCX1 and the calcium binding protein calretinin have emerged as new molecular effectors of delayed preconditioning in the brain. In the present study, we investigated whether NCX1 and calretinin cooperate within the preconditioned striatum to confer neurons greater resistance to degeneration. Confocal microscopy analysis revealed that NCX1 expression was upregulated in calretinin-positive interneurons in the rat striatum after tolerance induction. Consistently, coimmunoprecipitation assays performed on human SHSY-5Y cells, a neuronal cell line which constitutively expresses calretinin, revealed a binding between NCX1 and calretinin. Finally, silencing of calretinin expression, both in vitro and in vivo, significantly prevented preconditioning-induced neuroprotection. Interestingly, our biochemical and functional studies showed that the selective silencing of calretinin in brain cells significantly prevented not only the preconditioning-induced upregulation of NCX1 expression and activity but also the activation of the prosurvival protein kinase Akt, which is involved in calretinin and NCX1 protective actions. Collectively, our results indicate that the Na(+)/Ca(+2) exchanger NCX1 and the calcium binding protein calretinin cooperate within the striatum to confer tolerance against cerebral ischemia.